From the past, a number of improvements were made on two-piece golf balls. The main requirements on golf balls by players are concerned in distance, control and feel. Ordinary players make much of distance whereas skilled players set controllability above distance.
For golf balls, there were made a number of proposals for improvements in distance and controllability. For example, JP-A 10-127823 discloses a golf ball comprising a solid core and a cover which is improved in flight performance, controllability and feel by specifying the gage and JIS-C hardness of the cover and the type of solid core material and reducing the hardness difference between the solid core and the cover. JP-A 11-290479 discloses a golf ball which is improved in flight performance, controllability and feel by optimizing the hardness distribution and deflection or deformation of the core and the gage of the cover.
Since these proposals lay greatest store on distance increase, the cover is relatively hard. On use by skilled players, these balls receive less spin on approach shots and there is left a room for further improvement in controllability.
An object of the invention is to provide a two-piece solid golf ball which is susceptible to spin and easy to control upon approach shots and short iron shots, travels a long distance upon driver shots, gives a pleasant feel on any shot with driver, iron and putter clubs, and offers improved playability satisfying low-handicap players.
Regarding a golf ball comprising a solid core and a cover enclosing the core, the inventor made research to provide the golf ball with sufficient spin performance to satisfy the skilled players with respect to controllability.
The inventor has designed the golf ball such that the difference in JIS-C hardness between the center and the surface of the solid core (i.e., core surface hardness minus core center hardness) is at least 20 units, the cover has a gage of 1.3 to 2 mm and a Shore D hardness of up to 55, the difference in JIS-C hardness between the cover surface and the core surface (i.e., cover surface hardness minus core surface hardness) is up to 0, the total number of dimples is 360 to 492, and the percent dimple volume VR to be defined later is from 0.74% to 0.84%. Quite unexpectedly, not only the hardness balance in each structure of the solid core and the cover, but also the hardness balance of the overall ball are optimized, and as a consequence, the golf ball is susceptible to spin and easy to control upon approach shots and short iron shots, travels along a steadfast trajectory (neither dropping nor skying) upon driver shots and hence, a long distance, and gives a pleasant feel on any shot with driver, iron and putter clubs. Additionally, the ball offers a playability enough to satisfy low-handicap players who lay great store on control.
According to the invention, there is provided a two-piece solid golf ball comprising a solid core and a cover having a surface formed with a plurality of dimples, wherein the JIS-C hardness at the surface of the solid core minus the JIS-C hardness at the center of the solid core is at least 20 units; the cover has a gage of 1.3 to 2 mm and a Shore D hardness of up to 55, the JIS-C hardness at the cover surface minus the JIS-C hardness at the core surface is up to 0; the total number of dimples is 360 to 492; and the percent dimple volume VR is from 0.74% to 0.84% which is defined as a proportion (%) of the total of the volumes of dimple spaces each defined below a plane circumscribed by the dimple edge to the overall volume of a phantom sphere given on the assumption that the golf ball surface is free of dimples. Preferably, the solid core has a JIS-C hardness of up to 65 at its center.